Conventional polyolefins are resins excellent in chemical resistance and solvent resistance, but cannot be said to have sufficient rigidity and heat resistance, when their crystallinity is low.
In order to improve polyolefins in heat resistance and rigidity, there is therefore employed a method in which a nucleating agent is added or a polyolefin in a molten state is gradually cooled to increase the crystallinity. However, the effect thereof cannot be said to be satisfactory.
Apart from such conventional polyolefins, it is reported that a copolymer obtained by reaction of ethylene with a bulky monomer is excellent over conventional polyolefins in various properties such as heat resistance, etc. (U.S. Pat. No. 2,883,372 and Japanese Patent Publication No. 14910/1971).
The assignee of the present application already found that a cycloolefin random copolymer obtained by copolymerization of a specific cycloolefin as a bulky monomer and ethylene is excellent in heat resistance, thermal aging resistance, solvent resistance, dielectric properties and rigidity. On the basis of this finding, the assignee of the present application has already proposed inventions of random copolymers obtained from specific cycloolefins (Japanese Laid-Open Patent Publications Nos. 168708/1985, 98780/1986, 115912/1986, 115916/1986, 120816/1986 and 252407/1987).